The present invention relates to a storage medium disk driving apparatus used as, for example, a floppy disk drive which is an auxiliary storage apparatus of a computer, a word processor or the like.
A conventional storage medium disk driving apparatus of this type is illustrated in FIGS. 7 to 9. A centering projection 2 (a distal end portion of an output shaft) connected with a motor is formed on a central portion of the surface of a rotary plate 1. On a peripheral portion of the rotary plate 1, a recessed section 4 opened toward the top surface side and an opening section 5 opened through the bottom of the recessed section 4 are formed substantially along a peripheral direction of the rotary plate 1. A fixing plate 6 is provided inside of the recessed section 4. A proximal end portion 6b of the fixing plate 6 is pivotally attached on the peripheral portion of the rotary plate 1 through a fulcrum pin 7 in such a manner that a distal end portion 6a of the fixing plate 6 can be moved in and out of the opening section 5. The fixing plate 6 is biased in a direction away from the centering projection 2 by means of a spring (not shown), and is supported in contact with an outer peripheral portion 1a of the rotary plate 1. Thus, a cylindrical engaging projection 18 formed of a pin or a roller provided on the distal end portion 6a of the fixing plate 6 is positioned at a predetermined distance from the center of the rotary plate 1.
In the storage medium disk driving apparatus of the above-described structure, when a hub P of a storage medium disk is pressed, through a casing containing the storage medium disk, against the front surface of the rotary plate 1 in concentric and parallel relation, the distal end portion 6a of the fixing plate 6 is pressed by the hub P through the engaging projection 18 so as to cause elastic deformation of the fixing plate 6. In consequence, the distal end portion 6a is pushed in the opening section 5 of the rotary plate 1, and also, the centering projection 2 provided on the rotary plate 1 is engaged in a centering hole formed in the storage medium disk. Then, when rotating the rotary plate 1 at a low speed while sliding the engaging projection 18 on the hub P of the storage medium disk, the rotary plate 1 is rotated in concentric relation with the storage medium disk, and the engaging projection 18 located at the predetermined distance from the center of this rotation is engaged in an engaging hole formed in the storage medium disk. Since the hub P of the storage medium disk is no longer affected by the spring force to separate it from the rotary plate 1, the hub P of the storage medium disk is magnetically attracted by a magnet plate 1B provided on the surface of the rotary plate 1, and is brought into contact with a hub 3 of the rotary plate 1, thereby maintaining the engagement between the engaging projection 18 on the side of the rotary plate 1 and the engaging hole of the storage medium disk. Therefore, when the motor is driven, rotational torque is transmitted from the rotary plate 1 to the storage medium disk so that the storage medium disk will be rotated in concentric relation with the rotary plate 1.
However, when the hub P of the storage medium disk causes elastic deformation of the fixing plate 6 through the engaging projection 18 so that the distal end portion 6a of the fixing plate 6 is pushed in the opening section 5 of the rotary plate 1, the engaging projection 18 is inclined, as shown in FIG. 9, and the engaging projection 18 thus inclined is pressed against the hub P of the storage medium disk by the force of the fixing plate 6. In this condition, the rotary plate 1 is rotated idly with respect to the storage medium disk until the engaging projection 18 provided on the distal end portion 6a of the fixing plate 6 is engaged in the engaging hole formed in the hub P of the storage medium disk. Since the engaging projection 18 is shaped cylindrically, an edge 18a of the engaging projection 18 will be pressed against the hub P of the storage medium disk, depending upon an angle of inclination of the projection 18, so that the hub P of the storage medium disk will be damaged during a long time use. Due to such a damage of the hub P, it has been feared that the appearance of the storage medium disk will be spoiled, and that the magnetic surface of the storage medium disk will be damaged by metallic powder shaved from the hub P.
Moreover, when the distal end portion 6a of the fixing plate 6 is pressed by the hub P of the storage medium disk through the engaging projection 18, it penetrates through the opening section 5 of the rotary plate 1 and protrudes from the rear side of the rotary plate 1 owing to the elastic deformation of the fixing plate 6. If the impact when the hub P of the storage medium disk collides against the rotary plate 1 is large, the fixing plate 6 is momentarily bent by a large degree, and the distal end portion 6a largely protrudes from the rear side of the rotary plate 1, as shown in FIG. 9. Consequently, a part of the motor (e.g., a stator coil portion) brought into contact with the fixing plate 6 will be damaged, or the fixing plate 6 will be caught on some motor part so that the fixing plate 6 and the motor part will be damaged as a result of the subsequent rotation of the rotary plate 1. Because of such fears, the rotary plate 1 and the motor have conventionally been located to have a rather large space interposed therebetween, to thereby prevent the distal end portion 6a of the fixing plate 6 from contacting with motor parts.